1. Field of the Invention
The present invention relates to a pump apparatus of relatively small size, and more particularly to an improvement on the structure of a pump shaft drive portion of a pump apparatus.
2. Description of the Related Art
FIG. 1 shows a conventional compact pump apparatus for supplying operation fluid to a power steering apparatus of a vehicle. In the pump apparatus, a pump shaft 2 for driving a pump unit 5 disposed within a housing 1 is supported by a ball bearing 3 and a slide bearing 4; and a pulley 9 is fixed to one end of the pump shaft 2 projecting from the housing 1. A groove portion 9a is formed on the outer circumference of the pulley 9, around which a drive belt (not shown) is wound in order to transmit rotation of an engine of the vehicle to the pump shaft 2. As a result, the pump unit 5 is operated, so that operation fluid sucked from an inlet port 6 into the interior of the pump unit 5 is discharged from an outlet port 8 via a pressure chamber 7. Generally, the pump unit 5 is a balanced-type vane pump. In such a balanced-type vane pump, a plurality of (typically, two) suction ports are provided at symmetric positions; and a plurality of (typically, two) discharge ports are provided at symmetric positions. Therefore, radial forces generated within the pump unit 5 are cancelled out, so that almost no net load acts on the pump shaft 2. Accordingly, when merely the pump unit is considered, only one end of the pump shaft 2 is required to be supported by use of a bearing having a small load capacity.
However, since a large tension is applied to the drive belt in order to prevent slippage, the following problem occurs. That is, a large tensile force W1 acts on the pump shaft 2 perpendicularly at a position corresponding to a center plane L1 of the drive belt wound around the groove portion 9a of the pulley 9. Since the center plane L1 is located on the tip end side with respect to the ball bearing 3, a moment which inclines the pump shaft 2 is produced, and a force greater than the tensile force W1 acts on the ball bearing 3. Therefore, the ball bearing 3 must have a large load capacity; and the distance between the two bearings 3 and 4 must be increased. Therefore, the size of the bearing support portion of the housing 1 increases. This problem of the bearing support portion of the housing 1 having a large size is always present even in the case where both the bearings 3 and 4 are formed of ball bearings or slide bearings, or in the case where the bearings 3 and 4 are replaced with a single long slide bearing.
FIG. 2 shows another conventional pump apparatus of a compact type. In the pump apparatus, opposite ends of a pump shaft 11 for driving a pump unit 14 are supported by slide bearings 12 and 13, which are provided within a housing 10 to be located on the front and rear sides, respectively, of the pump unit 14; and a gear 17 is fixed to one end of the pump shaft 11 projecting from the housing 10. Rotation of an engine of the vehicle is transmitted to the gear 17 via a drive gear in meshing-engagement with a tooth portion 17a of the gear 17. Thus, the pump shaft 11 is rotated to drive the pump unit 14, whereby operation fluid sucked from an inlet port 15 into the interior of the pump unit 14 is discharged from an outlet port (not shown) via a pressure chamber 16.
In the conventional pump apparatus shown in FIG. 2, since the two slide bearings 12 and 13 for supporting the opposite ends of the pump shaft 11 are attached to two members which are fixed to each other by use of bolts, aligning the center axes of the slide bearings 12 and 13 is difficult, so that smooth rotation of the pump shaft 11 cannot be expected. Therefore, the conventional pump apparatus shown in FIG. 2 has drawbacks of increased frictional torque and generation of vibration and noise.
In view of the foregoing, an object of the present invention is to provide a pump apparatus which can solve the various problems involved in conventional pump apparatuses.
To achieve the above-object, the present invention provides a pump apparatus which is driven by drive force from a drive source, comprising a housing; a bearing member provided within a tip end portion of the housing; a pump shaft rotatably supported by the bearing member, one end of the pump shaft projecting from the tip end portion of the housing; a pump unit accommodated within the housing and operated through rotation of the pump shaft; and a drive member fixed to the one end of the pump shaft projecting from the housing and adapted to transfer drive force from the drive source to the pump shaft. The drive member includes a drive force input portion to which the drive force is transferred from the drive source. The center of the bearing member in the axial direction of the pump shaft coincides with-the center of the drive force input portion in the axial direction of the pump shaft.
Preferably, the drive member includes a boss portion fixed to the one end of the pump shaft projecting from the housing, and a rim portion integral with the boss portion, the rim portion being offset from the boss portion to cover at least a portion of the tip end portion of the housing; and the drive input portion is formed on the outer circumference of the rim portion.
Preferably, the bearing member consists of two bearings disposed adjacent to each other; and the center of the drive force input portion in the axial direction of the pump shaft is located between the respective centers of the two bearings in the axial direction of the pump shaft.
The drive force input portion may be a groove portion which is engaged with a drive belt extended between and wound around the groove portion and a pulley of the drive source. In this case, the center of the groove portion in the axial direction of the pump shaft is located between the respective centers of the two bearings in the axial direction of the pump shaft.
The drive force input portion may be a tooth portion which is in meshing-engaged with a drive gear of the drive source. In this case, the center of the tooth portion in the axial direction of the pump shaft is located between the respective centers of the two bearings in the axial direction of the pump shaft.
Preferably, the pump unit is a vane pump. More preferably, the vane pump is a balanced-type vane pump having a plurality of suction ports disposed symmetrically with respect to the pump shaft and a plurality of discharge ports disposed symmetrically with respect to the pump shaft.